In semiconductor technology, Group III-Group V (or III-V) semiconductor compounds may be used to form various integrated circuit (IC) devices, such as high power field-effect transistors (FETs), high frequency transistors, or high electron mobility transistors (HEMTs). A HEMT is a field effect transistor having a two dimensional electron gas (2-DEG) layer close to a junction between two materials with different band gaps (i.e., a heterojunction). The 2-DEG layer is used as the transistor channel instead of a doped region, as is generally the case for metal oxide semiconductor field effect transistors (MOSFETs). Compared with MOSFETs, HEMTs have a number of attractive properties such as high electron mobility and the ability to transmit signals at high frequencies.
When manufacturing HEMTs with III-V compounds, it is desirable to passivate the surface of the III-V compounds with a dielectric material layer (passivation layer) to prevent the III-V compounds from freely reacting with ambient air. Current methods of passivizing the surface of III-V compounds are not satisfactory in all respects. Sometimes, the interfacial density of states (Dit) at the interface between the passivation layer and the III-V compounds are undesirably high, causing device performance issues and reliability issues such as drain current degradation, large threshold voltage (Vt) fluctuation, and large off-current leakage. Accordingly, improvements in this area are needed.